The present invention relates generally to occupant restraint systems and more particularly to an integrated restraint system that is designed to significantly improve occupant safety by dissipating energy.
Safety belt restraint systems (or sub-systems) and air bag systems (or sub-systems) are often designed to meet separate and distinct safety criteria and performance standards and then used together as a combined system to provide occupant protection during frontal vehicle crashes and accidents. The performance, in terms of known, measurable occupant injury performance standards such as head injury criteria (HIC) and resultant chest acceleration of these combined systems may be less than the performance of the individual subsystem. This is shown below. It is believed that the degradation in performance, as manifested by increased occupant chest acceleration and related chest loading, is the result of an effective increased stiffness afforded by the seat belt system working in concert with the air bag system.
It is an object of the present invention to provide an improved occupant protection system. The invention herein describes an improvement is occupant performance in frontal accidents in comparison to the state of the art. The present invention proposes integrating in a single belted restraint system a very high output seat belt pretensioner 38 with an energy absorbing load limiting device 30. As will be seen from the description below the invention provides a surprising improvement to occupant protection as measured by performance standards such as HIC and chest acceleration. The benefit afforded by the present invention can be further enhanced by the addition of a web clamping device (such as a web clamping retractor) and/or the use of a low elongation webbing, that is, a webbing having an elongation of less than eight percent (8%). High output pretensioning as used herein refers to any pretensioning or belt tightening device which after operation provides a residual belt force (belt tension) of fifty pounds force or more. Such high output pretensioning device, according to the present invention, may include the buckle type of pretensioner in which the seat belt buckle is linearly moved or a retractor pretensioner in which the spool of the retractor is reverse wound. The concept of high output pretensioning is not available in current products and as described below results in the very early interaction of the seat belt with the occupant and provides a significant early acting restraining force, against the occupant during the accident or crash event. Reference is made to curve 300 FIG. 1 which shows the results of a physical test of a simulated prior art combined system verifying the benefits of the present invention. Curve 300 shows the resultant chest acceleration imparted to an occupant as a result of combining a prior art seat belt sub-system with air bag sub-system. As can be seen the peak accelerative occupant loading is about 56 g's. FIG. 2 is a bar graph showing the test results (chest acceleration) for a 30 mph simulated barrier crash of: a) the prior art seat belt sub-system (1), b) the prior art air bag system each tested along (2) c) the combined seat belt and air bag performance (3) and d) the performance (4) of the integrated systems in accordance with the present invention. FIG. 3 shows comparable data showing the HIC performance criteria. From the summary data shown in FIGS. 2 and 3 it can be seen that the peak accelerative loading and head injury criteria of the combined conventional system (g=56) exceeds that of either sub-system (g=45,41), this deficiency is avoided in the present invention. The results of the integrated system show that a chest acceleration (g) of 27 is attainable. Similar improvements in the HIC performance standards can also be seen in FIG. 3.
The deficiencies in the prior art combined system can be seen from the following. During the first few milli-seconds following a crash the occupant is protected only by the seat belt system as the air bag has not yet deployed sufficiently to contact the occupant. The protective restraining forces generated by the safety belt system (or subsystem) are highly dependent on the amount of permitted occupant movement, or excursion, which is strongly dependent on the geometric placement of the seat belt system components such as the anchor points, the shoulder belt D-ring (or belt guide as it is often called) and on the amount of belt slack that exists prior to the collision as well as the inherent force deflection properties of the particular seat belt system such as the elongation of the belt and deflection characteristics of a padded seat. The net result is that the restraint force is applied to the occupant late in the collision event and such force is very uneven (i.e. includes high peaks) as can be seen for example in curve 300 of FIG. 1. Convention seat belt pretensions or belt tighteners, as they are also known, of either the buckle type or retractor type offset, to some degree the effects of occupant excursion by eliminating some of the slack that may exist in the seat belt. As is known in the art, a conventional, low output pretensioner attempts to reduce slack in the belt system prior to any forward movement by the occupant which action typically occurs during the first ten (10) to twenty (20) milli-seconds after the beginning of the collision. As known in the art such pretensions do not produce high residual forces in the seat belt. This conclusion comes directly from the way pretensioners are tested and proven in actual practice. A typical test of a pretensioner includes wrapping a test dummy with a soft foam the thickness of which simulates a certain amount of slack that would exist in actual driving conditions. The forces developed during the operation of current pretensioners are generally only sufficiently to eliminate the slack (i.e. to compress the foam) prior to the time that any significant loads are developed in the seat belt or pretensioner due to the forward motion of the occupant. The low output pretensioner effectively manages occupant energy by providing a more uniform seat belt load application, thereby somewhat reducing the intensity of occupant or belt loading. However, the deficiency of the prior art pretensioner is that belt loads can increase the concentrated nature of the loading on the chest and as a result high chest deflections still occur. Other deficiencies with the prior art pretensioner are they do not generate a sufficient amount of residual force to effective manage occupant energy to control post crash movement of the occupant. While the pretensioner usually limits the forward velocity of the occupant it also inherently reduces the amount of permitted movement of the occupant. As such the occupant is not permitted to controllably move into the inflating air bag to permit more of the restraint load to be shared by the air bag.
Another effective means for enhancing occupant performance with a belt restraint is to use a load limiter. Load limiters effectively clip or limit peak loads that normally occur in the belt system by reintroducing a certain amount of slack in the seat belt system sometime after the accident has begun. The true benefit provided by a load limiter is in relation to combined seat belt and air bag performance which is to reduce the resultant restraint force imparted to the occupant. The load limited seat belt has the advantages of restraining the occupant's torso before it is contacted by the air bag. The load limited seat belt subsystem assists in mitigating the additive loading nature of the seat belt and air bag systems. A conventional load limited belt system may result in a reduction of chest acceleration of about 10%, depending on the specific application, see curve 304 of FIG. 4. As load limiting systems reintroduce slack into the belt, excursions are typically higher compared to a more conventional belt system.
High output pretensioning devices, in accordance with the present invention, can lower chest accelerations by at least 20% due to the smoother load application. Such devices are most effective, however, when used in combination with a high energy absorbing load limiting device which may be integrated within the same device or incorporated separately. Without the high output pretensioner, it is difficult to transmit load to the load limiting device early in the accident event thereby permitting energy absorbing to also occur early in the accident event. This early onset of load and energy absorption is critical to developing the pseudo constant acceleration process in the occupant response, which is felt to be near ideal.
Energy absorption or load limiting changes the characteristic of the seat belt, primarily the shoulder harness, by changing the force-deflection properties, usually resulting in a plateau or a nearly constant force device/system. The load limiter maintains restraint forces on the occupant which do not result in high accelerations or chest deflection. Further, the energy absorption mechanism can be tuned for optimal performance in a variety of environments. The strain rate sensitivity of an energy absorbing device can offset significantly severe impacts or help larger occupants by providing a greater restraint force during high energy occurrences. Further, the energy absorbing device can be tuned to a specific vehicle crash pulse to give the optimum shape to the load profile in the belt. For example, the energy absorbing device can be made stiff to correspond with high accelerations in the vehicle pulse and less stiff during low acceleration periods in order to achieve a pseudo constant acceleration in the occupant response, limiting lowers chest accelerations about 10-30% when compared to a conventional restraint system. When the proper energy absorbing device is combined with a high output pretensioner, occupant injury criteria can be reduced by 50% or more.
The true benefit of the integrated, present system is marked reductions in occupant injury response (HIC, chest accelerations, femur loads, chest deflection, neck response etc.). The absolute ideal occupant response to vehicle deceleration could be achieved by restraining the upper torso from an initial speed to a final speed in a linear fashion with the torso and head stopping just short of the instrument panel thereby avoiding interior contact. This constant acceleration process results in the lowest possible accelerations. Further, it is desirable to decelerate the head in the same manner in unison with the torso thereby causing low head injury criteria (HIC) and low neck injury. A system simultaneously utilizing high output pretensioning and load limiting is aimed at approximating this ideal situation in the following manner:
In accordance with the present invention the high output pretensioner applies a residual force in the belt of at least fifty pounds. This results in very early application of restraining force and control of the occupant velocity build-up with respect to the vehicle interior. The resultant chest acceleration shows (see curve 302 of FIG. 1) the effect of the high output pretensioner by increasing early in the event when compared to the normal case. Hip excursions are also reduced leading to very low femur loads. The ideal constant acceleration case is shown by phantom line 306. FIG. 5, shows a time trace showing the performance attainable with both a high output pretensioner and a load limiter.
Further in the present invention the load limiting device becomes activated at 350 lb-2000 lb dynamically. The load limiter can operate in this range at a constant force level or any force profile tuned to the particular environment within these ranges although it may go out of these ranges at times. The load limiter provides a plateau in the chest resultant acceleration by providing the means for a somewhat constant restraint force and therefore somewhat constant occupant accelerations (see FIG. 5). These accelerations are well below the typical accelerations for a conventional system and approach the ideal acceleration case. The same improvement for head injury criteria is shown in see FIG. 3 results in low neck injury. Because the energy absorbing device is used in combination with a high output pretensioner, very low occupant injury (low performance injury test data) is observed with occupant excursions that are comparable or below those measured with a typical seat belt system. The load limiter may also offer reduced resistance to occupant load at a time when the airbag system begins to offer significant restraint. The load limiter may also offer increasing restraint when significant occupant excursion has occurred and it is evident when the occupant is large or the crash is quite severe. Also, the load limiter may passively or actively adjust to these various test conditions to offer optimal resistance.
The combined and tuned system may be further enhanced by the addition of a web locking device to increase the initial stiffness of the system and ensure rapid onset of restraint force. The same effect can also be observed by the use of low elongation webbing which will also stiffen the system (see curve 308 of FIG. 6).
The early restraint of the chest followed by load limiting results in low accelerations in the chest and a better introduction of the occupant into the bag. That is, the head and torso are in unison as they engage the airbag at which time the restraint force of the bag controls both body parts. The net result is an improvement in both head injury criteria and neck response (not shown).
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.